In its broadest aspect, the present invention relates to an optical fiber transducer element whose light transmissivity and therefore its ability to absorb transmitted light changes in a smooth and gradual manner from end-to-end. Such an optical fiber transducer formed of material, such as certain polymers characterized by low density, low heat capacity, high coefficient of thermal expansion and a large Young's modulus, can be employed singly or in a group in a telephone receiver to produce vibration of an acoustical diaphragm over the audible range, in accordance with a more specific aspect of the invention. The linear thermal elongation and contraction of the light absorbent optical fiber element coupled between the diaphragm and the receiver terminal of the incoming optical fiber waveguide drives the diaphragm, which is resiliently mounted, in the audible frequency range from 300 Hz to 3300 Hz.
Opto-acoustical telephones are known in the prior art and are discussed in U.S. Pat. No. 4,002,897, Kleinman et al. This patent discloses a telephone receiver for converting optical signals through an optical fiber waveguide into audible acoustic signals including a small optical absorption chamber filled with optical absorbing material, such as dark fibrous material.
An object of the present invention is to simplify and improve on the construction of an opto-acoustic telephone receiver as exemplified in the Kleinman et al. patent, so as to render this type of telephone more practical, more economical to manufacture, and more reliable and efficient in its operation.
Prior U.S. Pat. No. 345,084, Spaulding, discloses an early sound transmitting and receiving device employing a longitudinally extensible and contractable carbon pencil-like rod element which is electrically stimulated. U.S. Pat. No. 254,642, Hale, discloses a telephone receiver having an elongated extensible and contractable iron core surrounded by a current carrying coil and coupled with a vibratory element. U.S. Pat. No. 3,314,306, Alabaster et al., shows an early electromagnetic telephone receiver having a resonant iron core element coupled to a resonant disc or diaphragm.
An important object of the invention is to provide an optical transducer for use in a telephone receiver or the like which can eliminate the necessity for copper wiring in the receiver and which renders the receiver more compatible with fiber optics transmission cables coming into wide usage.
Other objects and advantages of the invention will become apparent during the course of the following detailed description.